scholarly journals Atlantic Multidecadal Variability as a Modulator of Precipitation Variability in the Southwest United States

2018 ◽  
Vol 31 (14) ◽  
pp. 5525-5542 ◽  
Author(s):  
Dong Eun Lee ◽  
Mingfang Ting ◽  
Nicolas Vigaud ◽  
Yochanan Kushnir ◽  
Anthony G. Barnston
Keyword(s):  
United States ◽  
General Circulation ◽  
Thermal Structure ◽  
Daily Rainfall ◽  
General Circulation Models ◽  
The United States ◽  
Cold Season ◽  
Atlantic Multidecadal Variability ◽  
Multidecadal Variability ◽  
Upper Level

AbstractTwo independent atmospheric general circulation models reveal that the positive (negative) phase of Atlantic multidecadal variability (AMV) can reduce (amplify) the variance of the shorter time-scale (e.g., ENSO related) precipitation fluctuations in the United States, especially in the Southwest, as well as decrease (increase) the long-term seasonal mean precipitation for the cold season. The variance is modulated because of changes in 1) dry day frequency and 2) maximum daily rainfall intensity. With positive AMV forcing, the upper-level warming originating from the increased precipitation over the tropical Atlantic Ocean changes the mean vertical thermal structure over the United States continent to a profile less favorable for rain-inducing upward motions. In addition, a northerly low-level dry advection associated with the local overturning leaves less available column moisture for condensation and precipitation. The opposite conditions occur during cold AMV periods.

scholarly journals Projection of Future Heat Waves in the United States. Part I: Selecting a Climate Model Subset

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 587
Author(s):  
Javad Shafiei Shiva ◽  
David G. Chandler
Keyword(s):  
United States ◽  
General Circulation ◽  
Climate Model ◽  
Heat Waves ◽  
Well Being ◽  
General Circulation Models ◽  
The United States ◽  
Wide Range ◽  
Overall Performance ◽  
Impact Predictions

The widespread increase in global temperature is driving more frequent and more severe local heatwaves within the contiguous United States (CONUS). General circulation models (GCMs) show increasing, but spatially uneven trends in heatwave properties. However, the wide range of model outputs raises the question of the suitability of this method for indicating the future impacts of heatwaves on human health and well-being. This work examines the fitness of 32 models from CMIP5 and their ensemble median to predict a set of heatwave descriptors across the CONUS, by analyzing their capabilities in the simulation of historical heatwaves during 1950–2005. Then, we use a multi-criteria decision-making tool and rank the overall performance of each model for 10 locations with different climates. We found GCMs have different capabilities in the simulation of historical heatwave characteristics. In addition, we observed similar performances for GCMs over the areas with a partially similar climate. The ensemble model showed better performance in simulation of historical heatwave intensity in some locations, while other individual GCMs represented heatwave time-related components more similar to observations. These results are a step towards the use of contemporary weather models to guide heatwave impact predictions.

scholarly journals North American April tornado occurrences linked to global sea surface temperature anomalies

2019 ◽  
Vol 5 (8) ◽  
pp. eaaw9950 ◽  
Author(s):  
J.-E. Chu ◽  
A. Timmermann ◽  
J.-Y. Lee
Keyword(s):  
United States ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North American ◽  
General Circulation ◽  
Large Scale ◽  
Moisture Flux ◽  
General Circulation Models ◽  
The United States ◽  
Sea Surface

Annual tornado occurrences over North America display large interannual variability and a statistical linkage to sea surface temperature (SST) anomalies. However, the underlying physical mechanisms for this connection and its modulation in a rapidly varying seasonal environment still remain elusive. Using tornado data over the United States from 1954 to 2016 in combination with SST-forced atmospheric general circulation models, we show a robust dynamical linkage between global SST conditions in April, the emergence of the Pacific-North American teleconnection pattern (PNA), and the year-to-year tornado activity in the Southern Great Plains (SGP) region of the United States. Contrasting previous studies, we find that only in April SST-driven atmospheric circulation anomalies can effectively control the northward moisture-laden flow from the Gulf of Mexico, boosting low-level moisture flux convergence over the SGP. These strong large-scale connections are absent in other months because of the strong seasonality of the PNA and background moisture conditions.

scholarly journals Diurnal Characteristics of Rainfall over the Contiguous United States and Northern Mexico in the Dynamically Downscaled Reanalysis Dataset (US10)

2012 ◽  
Vol 13 (3) ◽  
pp. 1142-1148 ◽  
Author(s):  
Tomohito J. Yamada ◽  
Myong-In Lee ◽  
Masao Kanamitsu ◽  
Hideki Kanamaru
Keyword(s):  
United States ◽  
General Circulation ◽  
Summer Rainfall ◽  
General Circulation Models ◽  
The United States ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Northern Mexico ◽  
Convective Systems ◽  
Global Reanalysis

Abstract The diurnal characteristics of summer rainfall in the contiguous United States and northern Mexico were examined with the United States reanalysis for 5 years in 10-km horizontal resolution (US10), which is dynamically downscaled from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) Global Reanalysis 1 using the Regional Spectral Model (RSM). The hourly precipitation outputs demonstrate a realistic structure in the temporal evolution of the observed rainfall episodes and their magnitudes across the United States without any prescriptions of the observed rainfall to the global reanalysis and the downscaled regional reanalysis. Nighttime rainfall over the Great Plains associated with eastward-propagating, mesoscale convective systems originating from the Rocky Mountains is also represented realistically in US10, while the original reanalysis and most general circulation models (GCMs) have difficulties in capturing the series of nocturnal precipitation events in summer over the Plains. The results suggest an important role of the horizontal resolution of the model in resolving small-scale, propagating convective systems to improve the diurnal cycle of summer rainfall.

scholarly journals Hurricane Katrina (2005). Part II: Evolution and Hemispheric Impacts of a Diabatically Generated Warm Pool

2007 ◽  
Vol 135 (12) ◽  
pp. 3927-3949 ◽  
Author(s):  
Ron McTaggart-Cowan ◽  
Lance F. Bosart ◽  
John R. Gyakum ◽  
Eyad H. Atallah
Keyword(s):  
United States ◽  
Hurricane Katrina ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Flow Analysis ◽  
Warm Pool ◽  
The United States ◽  
The North ◽  
The North Atlantic ◽  
Upper Level

Abstract The landfall of Hurricane Katrina (2005) near New Orleans, Louisiana, on 29 August 2005 will be remembered as one of the worst natural disasters in the history of the United States. By comparison, the extratropical transition (ET) of the system as it accelerates poleward over the following days is innocuous and the system weakens until its eventual demise off the coast of Greenland. The extent of Katrina’s perturbation of the midlatitude flow would appear to be limited given the lack of reintensification or downstream development during ET. However, the slow progression of a strong upper-tropospheric warm pool across the North Atlantic Ocean in the week following Katrina’s landfall prompts the question of whether even a nonreintensifying ET event can lead to significant modification of the midlatitude flow. Analysis of Hurricane Katrina’s outflow layer after landfall suggests that it does not itself make up the long-lived midlatitude warm pool. However, the interaction between Katrina’s anticyclonic outflow and an approaching baroclinic trough is shown to establish an anomalous southwesterly conduit or “freeway” that injects a preexisting tropospheric warm pool over the southwestern United States into the midlatitudes. This warm pool reduces predictability in medium-range forecasts over the North Atlantic and Europe while simultaneously aiding in the development of Hurricanes Maria and Nate. The origin of the warm pool is shown to be the combination of anticyclonic upper-level features generated by eastern Pacific Hurricane Hilary and the south Asian anticyclone (SAA). The hemispheric nature of the connections involved with the development of the warm pool and its injection into the extratropics has an impact on forecasting, since the predictability issue associated with ET in this case involves far more than the potential reintensification of the transitioning system itself.

Multimodel Estimates of Atmospheric Response to Modes of SST Variability and Implications for Droughts

2010 ◽  
Vol 23 (16) ◽  
pp. 4327-4341 ◽  
Author(s):  
Philip J. Pegion ◽  
Arun Kumar
Keyword(s):  
United States ◽  
Climate Variability ◽  
General Circulation ◽  
Dominant Role ◽  
Circulation Model ◽  
The United States ◽  
Precipitation Variability ◽  
Climate Extreme ◽  
Central Pacific ◽  
Sst Variability

Abstract A set of idealized global model experiments was performed by several modeling centers as part of the Drought Working Group of the U.S. Climate Variability and Predictability component of the World Climate Research Programme (CLIVAR). The purpose of the experiments was to assess the role of the leading modes of sea surface temperature (SST) variability on the climate over the continents, with particular emphasis on the influence of SSTs on surface climate variability and droughts over the United States. An analysis based on several models gives more creditability to the results since it relies on the assessment of impacts that are robust across different models. Coordinated atmospheric general circulation model (AGCM) simulations forced with three modes of SST variability were analyzed. The results show that the SST-forced precipitation variability over the central United States is dominated by the SST mode with maximum loading in the central Pacific Ocean. The SST mode with loading in the Atlantic Ocean, and a mode that is dominated by trends in SSTs, lead to a smaller response. Based on the response to the idealized SSTs, the precipitation response for the twentieth century was also reconstructed. A comparison with the Atmospheric Model Intercomparison Project (AMIP) simulations forced with the observed SSTs illustrates that the reconstructed precipitation variability was similar to the one in the AMIP simulations, further supporting the conclusion that the SST modes identified in the present analysis play a dominant role in the precipitation variability over the United States. One notable exception is the Dust Bowl of the 1930s, and further analysis regarding this major climate extreme is discussed.

Present and Past Sea Surface Temperatures: A Recipe for Better Seasonal Climate Forecasts

2020 ◽  
Vol 35 (4) ◽  
pp. 1221-1234
Author(s):  
Matthew B. Switanek ◽  
Joseph J. Barsugli ◽  
Michael Scheuerer ◽  
Thomas M. Hamill
Keyword(s):  
United States ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
The United States ◽  
Cold Season ◽  
Sea Surface ◽  
Precipitation Forecast ◽  
The North ◽  
Model Ensembles ◽  
Tropical Sea

AbstractMonthly tropical sea surface temperature (SST) data are used as predictors to make statistical forecasts of cold season (November–March) precipitation and temperature for the contiguous United States. Through the use of the combined-lead sea surface temperature (CLSST) model, predictive information is discovered not just in recent SSTs but also from SSTs up to 18 months prior. We find that CLSST cold season forecast anomaly correlation skill is higher than that of the North American Multimodel Ensemble (NMME) and the SEAS5 model from the European Centre for Medium-Range Weather Forecasts (ECMWF) when averaged over the United States for both precipitation and 2-m air temperature. The precipitation forecast skill obtained by CLSST in parts of the Intermountain West is of particular interest because of its implications for water resources. In those regions, CLSST dramatically improves the skill over that of the dynamical model ensembles, which can be attributed to a robust statistical response of precipitation in this region to SST anomalies from the previous year in the tropical Pacific.

scholarly journals Regional Changes in the Interannual Variability of U.S. Warm Season Precipitation

2016 ◽  
Vol 29 (14) ◽  
pp. 5157-5173 ◽  
Author(s):  
Scott J. Weaver ◽  
Stephen Baxter ◽  
Kirstin Harnos
Keyword(s):  
United States ◽  
The United States ◽  
Precipitation Variability ◽  
Height Anomaly ◽  
Epochal Change ◽  
Upper Level ◽  
Recent Epoch ◽  
Level Height ◽  
Circulation Changes

Abstract Intensification of regional springtime precipitation variability over the United States and the role of North American low-level jets (NALLJs) are investigated for the 1950–2010 period. The analysis reveals that the primary modes of NALLJ fluctuations are related to the strengthening of AMJ precipitation variability over the northern Great Plains and southeastern United States during the last 60 years. Examination of the epochal change in NALLJ variations shows a stronger connectivity to SST variability during 1980–2010 than in the 1950–79 period. In the context of the first three NALLJ variability modes it appears that the role of decadal SST variations (NALLJ mode 1) and the recent emergence of tropical Pacific connectivity (NALLJ modes 1 and 2) via SST-induced atmospheric heating and large-scale circulation changes may act to strengthen and spatially shift the NALLJ variability modes southward and/or eastward, intensifying regional precipitation variability in the recent epoch. Although notable NALLJ variability also exists in the earlier epoch, the upper-level height field is significantly lacking in meridional gradients, leading to weak upper-level zonal wind anomalies over the United States and diminished NALLJ variability. Conversely, the intensified and spatially shifted upper-level height anomaly in the recent epoch produces enhanced meridional height gradients in all three modes, strengthening NALLJ variability—highlighting that seemingly subtle shifts in hemispheric-scale atmospheric circulation changes can have important impacts on regional climate variability and change.

scholarly journals Implement and Analysis on Current Ecosystem Classification in Western Utah of the United States and Yukon Territory of Canada

2021 ◽  
Author(s):  
YanQing Zhang ◽  
Neil E. West
Keyword(s):  
United States ◽  
North America ◽  
The United States ◽  
Yukon Territory ◽  
Ecological Site ◽  
Ecosystem Classification ◽  
Natural Land ◽  
Upper Level ◽  
Abiotic And Biotic Factors ◽  
Vegetation Stand

The study cases in western Utah of the United States and Yukon Territory of Canada have more natural land and conservative ecosystems in North America. The ecosystem classification of land (ECL) in these two ecoregions had been analyzed and validated through implementation. A full ECL case study was accomplished and examined with eight upper levels of ECOMAP plus ecological site and vegetation stand in Western Utah, the US. Theoretically, applying Köppen climate system classification, Bailey’s Domain and Division were applied to the United States, North America, and world continents. However, Canada’s continental upper level ecoregion framework defined the ecological Mozaic on a sub-continental scale, representing an area of the hierarchical ecological units characterized by interactive and adjusting abiotic and biotic factors. Using Bailey’s Domain as the top level of Canada’s territorial ecoregion was recommended. Eight levels of ELCs were established for Yukon Territory, Canada. Thus, the second study case recommends integrating the ecosystem approaches with Bailey’s upper level ECL, broad ecosystem classification, and objectively defined ecological site in different countries, or ecoregions. Our study cases had exemplified the implementations with a full ELCs in Bailey’s 300 Dry Domain and 100 Polar Domain.

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